This invention relates to a method of measuring the alignment of one surface relative to another and, more particularly, to a method for determining the angular alignment of transducer mounting surfaces relative to one another.
It is necessary for a pilot of an aircraft to determine whether the aircraft's weight and balance are within the safe operating limits or boundaries of the aircraft. A system for providing such an indication to the pilot is disclosed in U.S. Pat. No. 4,312,042, assigned to the assignee of this application. This system utilizes two or more inclinometers to measure the bend in a structural member, such as a landing gear element, a wing, or a fuselage section, due to the loading of the aircraft. Typically, an inclinometer is mounted at each end of the structural member on transducer mounting surfaces which are fixed within or to the structural member.
However, if the transducer mounting surfaces are misaligned, i.e. out of parallel, with respect to each other, in turn causing a misalignment of the transducers mounted on the structural member, then rotations of the structural member about its longitudinal axis will cause second order angle effects which will be sensed by the transducers. These angle effects typically cause weight errors in the system and hence a false indication of aircraft loading and/or balance.
In the past, the transducer mounting surfaces were initially installed in or on the structural member by sight approximation to align the transducer surfaces. Typically, this alignment resulted in angular errors of the placement of one transducer mounting surface relative to another of up to .+-.3.5.degree., resulting in the above-noted degradation of the accuracy of the weight and balance system.
The problem of physically measuring the alignment of the mounting surfaces relative to one another becomes evident when one considers the physical surroundings and what the accuracy requirements are of measuring the surfaces for parallelism. One problem is that the two transducer mounting surfaces may be up to approximately 80 inches apart in some aircraft and facing in opposite directions. Another problem is that a structural member itself is often located between the two surfaces, further compounding the difficulty of accomplishing the desired result.
Typically, the mounting surfaces for the transducers must be aligned with respect to one another within a very close range, typically .+-.0.1.degree. in the horizontal plane, in order to reduce weight errors to an insignificant degree. This requirement is equivalent to measuring a linear distance of approximately 0.0041" from 80" away, and with the obstacles present as noted above.
One proposed solution is to use a precision surveying type transit scope and mirrors. However, this has proved to be impractical since the human eye is not able to accurately distinguish the resolution required at 80", even with the magnification of a precision scope.